Beyond what CAMPYBOB stated ...
With regard to whether or not your bike is a Bianchi ...
Maybe yes, maybe no ...
But, I don't see why it couldn't be OR what precludes it from being one ...
So, FWIW, I would say that it probably is ...
- now, it is certainly possible to buy replacement decals & slap them on ANY frame. but ...
- nonetheless, Bianchi sold frames across the entire pricing spectrum ... for over 100 years!
Regardless, while the rear seat stays may not look like whatever the particular individual is specifically familiar with (was he referring to the rear rack tabs which would not have been found on a true "racing" bike of that particular vintage?) , it doesn't mean that the bike isn't a Bianchi UNLESS it has something really distinctive such as a "custom" bridge with another bike manufacturer's name cast into it, or elsewhere on the frame.
In other words, while the individual may have been correct, it could also be said that identifying and excluding the origin of the bike's origin based on the seat stays is like the individual saying that it isn't a Bianchi because it isn't painted Celeste Green ...
To satisfy your curiosity, you can contact Bianchi and they will probably be able to tell you whether or not the bike IS-or-ISN'T actually a Bianchi ... and, if it is, then they will probably provide you with more specifics -- year (e.g., 1979), model, etc.
Now, by today's "standards" the bike may be cosmetically too large for you, but if your feet can reach the pedals AND you do not feel to stretched out on it, then its size is more of a cosmetic issue BECAUSE the amount of seatpost exposure which your bike currently has was not atypical at one time (i.e., pre-1970).
If you feel too stretched out, then a $15-to-$20 stem will probably "fix" the problem, BTW.
